The number of items prescribed rose to 94.9 million, up 3.8 per cent from 2010-11, with the vast majority of prescriptions written by GPs.

The Royal College of Nursing said its analysis found nine out of 14 health boards overspent on prescribing in the financial year 2011-12.

RCN Scotland director Theresa Fyffe said: “The latest rise in prescribing costs, on top of years of growing spend on prescribing, comes when the overall health budget is virtually at a standstill.

The pressure is mounting on health boards to make increasingly difficult decisions to balance books while maintaining quality services to meet growing patient demand

RCN Scotland director Theresa Fyffe

“The pressure is mounting on health boards to make increasingly difficult decisions to balance books while maintaining quality services to meet growing patient demand. That’s why we’ve consistently called for health boards to be more open and honest about what they currently spend their money on and what their plans for the future consist of.

“Only then will they have a chance of bringing the public, patients and staff with them when they make difficult decisions to change the way health services are provided.”

The health budget has been protected in Scotland but public spending watchdog Audit Scotland said annual rises in funding must compete with pressures from pay, fuel and drug prescribing, alongside an ageing population. Scottish Tory health spokesman Jackson Carlaw said: “The rise in free prescriptions is simply unsustainable when the health budget is under so much stress.

“We have heard numerous health boards at the Scottish Parliament saying that the cost is starting to have an impact on frontline services.”

A spokeswoman for the Scottish Government said: “We continue to collaborate with NHS boards to ensure that prescribing in primary care is effective, economic and efficient.

“It’s important to note that significant resources are available for prescribing in primary care year on year, which take account of prescribing trends and other influencing factors.”